1734 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
INTRODUCTION
Coltan ore contains two refractory metals of technologi-
cal importance, namely tantalum (Ta) and niobium (Nb).
Both metals are very similar in terms of their chemical
and physical properties which makes their separation and
purification difficult (Ayanda and Adekola, 2011). Their
intrinsic properties, such as very high corrosion resistance,
superconductivity, high electrical capacity, and biocompat-
ibility make them highly strategic metals (Shikika et al.,
2020). They have different applications, although being
always found together in their ores. Niobium is mainly
used in the production of ferroniobium for the manufac-
ture of micro-alloyed steels which are used in the construc-
tion, ships, and refinery equipment, etc. Tantalum is the
main component of miniaturized capacitors used in micro-
electronics. Current industrial processes for the purification
and separation of tantalum (Ta) and niobium (Nb) bearing
columbite-tantalite (coltan) ores rely exclusively on hydro-
fluoric acid leaching and solvent extraction using MIBK
(Shikika, 2023). However, due to the harmful effect of
HF, more environmentally friendly processes deserve to be
developed. Therefore, emerging processes such as alkaline
and oxalic ones are increasingly being studied during the
last decades.
Research has been conducted to extract Ta and/or Nb
from leachates containing oxalic acid. Yang et al. (2015)
reported on extraction of Nb from oxalic acid aqueous
media using a N235-type extractant (R3N, with R= C8-10)
diluted in octyl alcohol. However, the Nb stripping was not
addressed in this study. Sun et al. (2021) reported on separa-
tion and purification of Ti and Nb from oxalic-sulfuric acid
media using N235 and MIBK as extractants. Djordjević et
al. (1966) studied the selectivity of amines including tri-
n-octyl amine (TOA), tri-n-decyl amine (TDA), and tri-
n-dodecyl amine (TDDA) diluted in carbon tetrachloride
(CCl4) during the extraction of Ta and Nb from a synthetic
oxalic solution. Distribution coefficients of about 820 for
Nb and 500, 740 and 690 for Ta were reported for the three
amines TOA, TDA and TDDA respectively. Bhattacharyya
and Ganguly (1986) studied the extraction of Ta and Nb
from oxalic and hydrochloric acid media using a di(2-
ethylhexyl) phosphoric acid (HDEHP) extractant diluted
in n-heptane. The obtained results enabled approximately
85% of Ta to be extracted.
However, the conventional solvent extraction process
is economically and ecologically unfavorable, as it gener-
ates toxic side products due to the use of a large amount
of solvents and their losses resulting from volatility or
partial blending with the aqueous phase (Turkowska et
al., 2022). This work aims to investigate the feasibility of
efficient purification and separation of Ta(V) and Nb(V)
from oxalic acid media using solvent extraction employing
Aliquat ® 336 extractant and conceptualize a process as an
outcome.
MATERIALS AND METHODS
Leachates and Reagents
The aqueous phase (pH~1.1) used in this study presents a
combined solution generated during oxalic leaching tests of
Ta-Nb precipitates as described in our previous study
(Shikika et al., 2022). The chemical composition of this
stock solution is given in Table 1.
All chemical reagents used, namely sulfuric acid (95%),
nitric acid (65%), were of analytical grade, purchased from
VWR (Avantor). Deionized water was used for aqueous
solutions preparation. Isodecanol (98%) and Aliquat ®
336 (98%) of analytical grade were purchased from Merck
KGaA (Germany) and used without further purification,
while kerosene was used as diluent. For the solvent extrac-
tion using Aliquat ® 336, the organic phase consisted of
Aliquat ® 336 (extractant), a modifier (isodecanol, 3% v/v)
and kerosene as diluent. Due to the elevated viscosity of the
Aliquat ®336, the mixture was stirred for at least 15 minutes
to ensure complete dissolution prior to tests begin.
Extraction and Stripping Procedures
The extraction procedure consisted in contacting inside
250 mL beaker equal volumes of aqueous and organic
phases under the selected experimental conditions. The
both phases were agitated at 400 rpm using a magnetic stir-
rer. Once equilibrium time reached, the phases were sepa-
rated through a separating funnel and the resulting aqueous
phase was assayed as described in the following section.
Stripping experiments were conducted to back-extract
and separate Ta and Nb from the Aliquat ® loaded organic
phases. The latter were generated using the optimal condi-
tions being found during the solvent extraction of Ta and
Nb. Stripping was performed by contacting equal volumes
of the loaded organic and aqueous solutions. Agitation
speed and contact time for phases mixing were 400 rpm
and 10 minutes respectively. Following phases separation
through a separating funnel, the resulting aqueous phase
was also assayed.
Table 1. Chemical composition of the aqueous stock
solutions (mg/L)
Elements Ta Nb Fe Mn Ca
Concentration, mg/L 1977 10513 291 67 610
INTRODUCTION
Coltan ore contains two refractory metals of technologi-
cal importance, namely tantalum (Ta) and niobium (Nb).
Both metals are very similar in terms of their chemical
and physical properties which makes their separation and
purification difficult (Ayanda and Adekola, 2011). Their
intrinsic properties, such as very high corrosion resistance,
superconductivity, high electrical capacity, and biocompat-
ibility make them highly strategic metals (Shikika et al.,
2020). They have different applications, although being
always found together in their ores. Niobium is mainly
used in the production of ferroniobium for the manufac-
ture of micro-alloyed steels which are used in the construc-
tion, ships, and refinery equipment, etc. Tantalum is the
main component of miniaturized capacitors used in micro-
electronics. Current industrial processes for the purification
and separation of tantalum (Ta) and niobium (Nb) bearing
columbite-tantalite (coltan) ores rely exclusively on hydro-
fluoric acid leaching and solvent extraction using MIBK
(Shikika, 2023). However, due to the harmful effect of
HF, more environmentally friendly processes deserve to be
developed. Therefore, emerging processes such as alkaline
and oxalic ones are increasingly being studied during the
last decades.
Research has been conducted to extract Ta and/or Nb
from leachates containing oxalic acid. Yang et al. (2015)
reported on extraction of Nb from oxalic acid aqueous
media using a N235-type extractant (R3N, with R= C8-10)
diluted in octyl alcohol. However, the Nb stripping was not
addressed in this study. Sun et al. (2021) reported on separa-
tion and purification of Ti and Nb from oxalic-sulfuric acid
media using N235 and MIBK as extractants. Djordjević et
al. (1966) studied the selectivity of amines including tri-
n-octyl amine (TOA), tri-n-decyl amine (TDA), and tri-
n-dodecyl amine (TDDA) diluted in carbon tetrachloride
(CCl4) during the extraction of Ta and Nb from a synthetic
oxalic solution. Distribution coefficients of about 820 for
Nb and 500, 740 and 690 for Ta were reported for the three
amines TOA, TDA and TDDA respectively. Bhattacharyya
and Ganguly (1986) studied the extraction of Ta and Nb
from oxalic and hydrochloric acid media using a di(2-
ethylhexyl) phosphoric acid (HDEHP) extractant diluted
in n-heptane. The obtained results enabled approximately
85% of Ta to be extracted.
However, the conventional solvent extraction process
is economically and ecologically unfavorable, as it gener-
ates toxic side products due to the use of a large amount
of solvents and their losses resulting from volatility or
partial blending with the aqueous phase (Turkowska et
al., 2022). This work aims to investigate the feasibility of
efficient purification and separation of Ta(V) and Nb(V)
from oxalic acid media using solvent extraction employing
Aliquat ® 336 extractant and conceptualize a process as an
outcome.
MATERIALS AND METHODS
Leachates and Reagents
The aqueous phase (pH~1.1) used in this study presents a
combined solution generated during oxalic leaching tests of
Ta-Nb precipitates as described in our previous study
(Shikika et al., 2022). The chemical composition of this
stock solution is given in Table 1.
All chemical reagents used, namely sulfuric acid (95%),
nitric acid (65%), were of analytical grade, purchased from
VWR (Avantor). Deionized water was used for aqueous
solutions preparation. Isodecanol (98%) and Aliquat ®
336 (98%) of analytical grade were purchased from Merck
KGaA (Germany) and used without further purification,
while kerosene was used as diluent. For the solvent extrac-
tion using Aliquat ® 336, the organic phase consisted of
Aliquat ® 336 (extractant), a modifier (isodecanol, 3% v/v)
and kerosene as diluent. Due to the elevated viscosity of the
Aliquat ®336, the mixture was stirred for at least 15 minutes
to ensure complete dissolution prior to tests begin.
Extraction and Stripping Procedures
The extraction procedure consisted in contacting inside
250 mL beaker equal volumes of aqueous and organic
phases under the selected experimental conditions. The
both phases were agitated at 400 rpm using a magnetic stir-
rer. Once equilibrium time reached, the phases were sepa-
rated through a separating funnel and the resulting aqueous
phase was assayed as described in the following section.
Stripping experiments were conducted to back-extract
and separate Ta and Nb from the Aliquat ® loaded organic
phases. The latter were generated using the optimal condi-
tions being found during the solvent extraction of Ta and
Nb. Stripping was performed by contacting equal volumes
of the loaded organic and aqueous solutions. Agitation
speed and contact time for phases mixing were 400 rpm
and 10 minutes respectively. Following phases separation
through a separating funnel, the resulting aqueous phase
was also assayed.
Table 1. Chemical composition of the aqueous stock
solutions (mg/L)
Elements Ta Nb Fe Mn Ca
Concentration, mg/L 1977 10513 291 67 610